Linux EC2 instances in two AZs of the same VPC run an NFS-aware application reading and writing the same shared files. Each AZ has an application instance; surviving instances must access the same files after loss of one AZ.
Do not rewrite the application for object APIs or operate a file server yourself. Prepare client retries, NFS access permissions, and security groups.
Which configuration is most appropriate?
Use EFS Regional and mount targets in each consuming AZ to prepare redundant shared-file storage and access paths.
Detailed explanation
Matching path names do not share separate volume contents; this does not provide the same shared files.
Matching path names do not share separate volume contents; this does not provide the same shared files.
Redundant storage and access paths are separate. Loss of the target AZ leaves surviving clients without a local target path.
Redundant storage and access paths are separate. Loss of the target AZ leaves surviving clients without a local target path.
Cross-AZ mounting is possible, but data stays in one AZ and is not resilient to loss of that storage AZ.
Cross-AZ mounting is possible, but data stays in one AZ and is not resilient to loss of that storage AZ.
This provides redundant data storage and a surviving local access path; client and target network permissions are also required.
This provides redundant data storage and a surviving local access path; client and target network permissions are also required.
Check official documentation
Compare the following points with the official documentation.
Review the linked AWS documentation for storage, connection paths, scaling scope, and prerequisites.
Official references
- Official documentation 1
- Official documentation 2
- Official documentation 3
- Official documentation 4
- Official documentation 5
What to confirm
Explain the operational limits of the alternatives and the application checks needed after configuration.
Key points
- EFS Regional
- Mount target
- Shared file
Notes
- Environment: AWS SOA-C03 exam guide and the linked AWS documentation
- Reviewed against the linked AWS documentation on 2026-10-06.
Foundation review
Regional versus One Zone
Regional stores data across multiple AZs; One Zone stores it in one AZ. Connecting to One Zone from another AZ does not add storage redundancy. Applications must handle NFS permissions, consistency, and locking; individual object downloads do not provide the same file-access model.
Prepare access paths as well as storage
Regional supports one mount target per AZ. Multiple subnets in an AZ can share that target; a target per subnet is unnecessary. Allow client outbound and target inbound TCP 2049, and verify startup mounting and retries. Surviving application instances and paths must remain operational; this is not a guarantee of uninterrupted existing access.